1. Field of the Invention
This invention relates to the acquisition of geophysical data including that produced by induced electromagnetic effect, seismic, and coupled phenomena thereto, such as electromagnetic propagation velocity dispersion effects in lossy media.
2. Description of the Prior Art
It is a well known phenomena that electromagnetic fields impinge on the earth's surface at all times and create both electric fields and magnetic fields that are detectable utilizing proper techniques and apparatus. Such fields, for example, are generated by solar activity and ionospheric activity in the earth's own atmosphere. It has been known since the 1930's that seismic waves generated in seismic exploration techniques can generate Induced Electrokinetic (IEK) effects in the form of electromagnetic waves emanating from the earth formation structures impinged upon by the seismic waves. Prior art patents, such as U.S. Pat. No. 3,975,674 to McEuen, have taught that the electrokinetic effect radiation may be used for determining, remotely, resistivity and equivalent salinity of fluids saturating pore space in subterranean formations.
Although the McEuen patent and other more recent patents have indicated an interest in prospecting for geophysical data using induced electrokinetic (IEK) effect electromagnetic radiation, most researchers have conceded that the depth of investigation of such techniques is limited. Papers as lately as the mid 1990's have indicated that a depth of approximately 500 meters from the earth's surface was about the limit from which useful data concerning induced electrokinetic (IEK) effect electromagnetic radiation.
During the interim since the 1930's, (and the discovery of the electrokinetic effect in its first publication), seismic data processing has undergone remarkable advances. More sensitive detectors, two dimensional arrays of detectors on land, and offshore exploration by seismic streamer cable towing ships together with the advancement of computer technology have enabled seismic data to be processed and corrected for the time migration or “move out” of such data. This correction is needed to convert time line arrival data onto actual depth due to acoustic wave velocity dispersion and velocity differences in subsurface media. The earth's true acoustic velocity profile in its layers is usually unknown at the time of seismic exploration.
The present invention incorporates techniques for acquisition and processing of seismic data when necessary in order to verify or enhance induced electrokinetic electromagnetic radiation effects which are measured simultaneously therewith or in timed sequence therewith at the earth's surface. Experimental data gathered with the system of the present invention and practicing the methods thereof have successfully differentiated between dry hole prospects and producing wells in known hydrocarbon producing formations. Further these techniques have explained the discrepancies between the initial seismic survey data and the later induced electrokinetic electromagnetic radiation survey data over the same area.
Moreover, the present invention provides a means for directly detecting hydrocarbon interfaces at depth down to 5000 meters. This sharply contrasts with the previous published results as late as the mid 1990's and indicates that the invention is a significant advance in the art of geophysical prospecting.